1. Field of the Invention
The present invention relates generally to a magnetic disk cartridge, and more particularly to a small magnetic disk cartridge that is inserted and loaded in a disk drive provided in small electronic equipment such as a digital camera, a laptop computer, etc.
2. Description of the Related Art
To record or reproduce information, a recording medium is removably inserted in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop computer, etc. Such recording media in practical use are of a semiconductor memory type, a hard disk type, an optical disk type, a magnetic disk type (e.g., a floppy disk type), etc.
Among these recording media, semiconductor memories are most widely used because they are easy to handle and have a relatively large recording capacity. However, they are relatively expensive. Because of this, in digital cameras employing the semiconductor memory, the photographed image data is transferred to a PC and stored, the data is deleted from the memory, and the semiconductor memory is repeatedly used.
Hard disks are similarly expensive, although some of them can store 340 megabytes (MB) of data or 1 gigabytes (GB) of data. Because of this, data is transferred to another device and stored, and hard disks are repeatedly used.
Optical disks have a large recording capacity for their size. For example, an optical disk with a size of 35 mm×41 mm×11 mm can store 260 MB of data. Optical disks with a recording capacity of 512 MB are about to be realized. However, optical disks have the disadvantage that the recording speed is slow, because their writing time is time-consuming.
Some magnetic disks such as a floppy disk have a small size of 50 mm×55 mm×2 mm. Such a small magnetic disk can be exchangeably loaded in a disk drive of a size that can be inserted into the card slot of a PC, etc. However, the recording capacity is as small as 40 MB and insufficient to record image data photographed by a camera. In addition, the size is not suitable for digital cameras.
With the spread of PCs, digital cameras have spread rapidly in recent years because of the simplicity of recording, enhancement in picture quality due to the development of imaging elements, possibility of data deletion and transmission, recording capacity size, etc. However, the method of use is restricted, because recording media are limited in cost and recording capacity, as described above. For instance, since recording media are very expensive, a single camera has only a single recording medium, which is repeatedly used. That is, when the recording medium is filled with data, the data is transferred to a PC and deleted. Because of this, there are cases where the recording medium is filled up during a trip. In such a case, the recording medium cannot be stored along with data and cannot be given away to a person.
The realization of a recording medium which is large in recording capacity, low in cost, and small in size so that the data photographed by a digital camera can be stored or given away to a person is desired. With regard to PCs as well, the realization of a recording medium which is large in recording capacity, low in cost, and small in size so that data can be stored thereon and handed to a person is desired.
To meet the aforementioned demands, it is contemplated that the above-described inexpensive small large-capacity recording medium may comprise a card-type disk drive which is loaded in electronic equipment such as a PC and a digital camera, and a magnetic disk cartridge which is loaded in the card-type disk drive. That is, it is contemplated that such a magnetic disk cartridge may include a housing in which a flexible magnetic disk is rotatably housed, and have a recording capacity of 200 MB or larger. Examples of high density magnetic recording media are a recording medium with a thin metal film formed by vapor deposition, a recording medium with a thin metal film formed by sputtering, and a recording medium employing barium ferrite powder or ferromagnetic magnetic powder. An example of a high density magnetic recording medium employing barium ferrite powder is disclosed in Japanese Patent Application No. 2001-312864.
The “high density magnetic recording medium employing barium ferrite powder” is a magnetic disk containing barium ferrite powder in a magnetic layer, and employs a material capable of high-recording density. The magnetic disk may comprise a magnetic recording medium disclosed in, for example, Japanese Patent Application No. 2001-205290. The magnetic recording medium has a non-magnetic layer which includes both non-magnetic powder and a binder, and a magnetic layer which includes both ferromagnetic powder (which is ferromagnetic metal powder or hexagonal-system ferrite powder) and a binder on at least one surface of a nonmagnetic substrate. The non-magnetic layer and the magnetic layer are formed on at least one side of a non-magnetic supporting body in the recited order. In the non-magnetic layer, the quantity of carbon black whose average particle diameter is 10 to 30 nm is 10 to 50 weight parts with respect to 100 weight parts of the aforementioned non-magnetic powder. The thickness of the magnetic layer is 0.2 μm or less. According to a microanalysis by an electron beam, the standard deviation (b) of the strength of an element with respect to an average strength (a) resulting from ferromagnetic powder is 0.03≦b/a≦0.4. The center plane average roughness Ra of the magnetic layer is 5 nm or less, and the 10-point average roughness Rz is 40 nm or less. In a magnetic disk employing the above-described material, information is recorded or reproduced by a magnetic head such as an MR head capable of high-recording density.
The above-described magnetic recording medium can have a recording capacity of 200 MB or larger, preferably 500 MB or larger. Therefore, if a still image has 1 MB of data per sheet, the magnetic recording medium can store 500 sheets. In the case of a dynamic image, the magnetic recording medium can store image contents of about 30 minutes. Thus, the magnetic recording medium can store a dynamic image photographed by a digital camera, and a dynamic image transmitted by a portable telephone. As a result, users can conveniently use the magnetic recording medium. Furthermore, the magnetic recording medium can be conveniently used in PCs as an inexpensive large-capacity recording medium. Thus, the convenience is great.
Preferred examples of disk drives in the present specification include disk drives incorporated in PCs, digital cameras, etc., as well as other types of disk drives. In the case of PCs, there are a disk drive 1′ shown in FIG. 32A, and disk drives incorporated in a PC card, such as “click!” (registered trademark). The disk drive 1′ is connected electrically with a socket 7 of the receiving portion of a card 6 that is inserted in a PC card slot provided in a PC. In the case of a digital camera 8, as shown in FIG. 32B, there is a small disk drive 1′ that is connected electrically with the socket of the receiving portion 9 of the camera 8. Therefore, the small disk drive 1′ is extremely small in size and has, for example, a length of 38 to 55 mm, a width of 35 to 51 mm, and a thickness of 3 to 5 mm. A magnetic disk cartridge 10′ has, for example, a length and a width of 25 to 36 mm and a thickness of 1 to 3 mm.
Incidentally, it has been proposed that the housing of such a subminiature magnetic disk cartridge is formed into the shape of a disk so that the magnetic recording medium can be handled like a coin. That is, if the magnetic recording medium can be handled with the same ease that a coin is inserted into the slot of a vending machine, the convenience can be enhanced.
In such a type of magnetic recording medium, the magnetic disk is provided in a housing and protected, as with conventional floppy disks. When the magnetic recording medium is loaded in a small disk drive, and information is recorded or reproduced, a shutter provided in the housing is moved so that the magnetic disk is exposed, thereby providing access thereto.
Even in the case of the housing formed into the shape of a disk, it is necessary to insert the housing in a predetermined direction so that information can be recorded or reproduced. If the housing is formed into the shape of a disk, however, the housing can be inserted into a disk drive regardless of the position of the shutter, because it has no directionality. That is, there is a possibility that the magnetic disk cartridge will be inserted into a disk drive in a direction where information recording and reproduction cannot be performed.